1. Field of the Invention
This invention relates generally to the field of fabrication of semiconductor devices and, more particularly, to a physical-vapor deposition (PVD) apparatus and method of using the apparatus.
2. Description of the Related Art
Sputtering, a type of physical vapor deposition, is widely used in semiconductor manufacturing to deposit thin metal or insulating films on semiconductor wafers.
Conventional sputtering apparatus 11 shown in FIG. 1 includes a process chamber 10 enclosing a target 12 affixed to the top thereof and a wafer pedestal 14 where a semiconductor wafer 16 rests during deposition. The target 12 is formed of a deposition material to be deposited. A lower shield 18 and an upper shield 20 are positioned within the chamber 10 such that they are electrically insulated from the chamber 10 and able to take on a floating electrical potential associated with the potential of the plasma of a gas, e.g. argon, generated within the chamber 10. Additionally, a cover ring 22 is engaged with the lower shield 18 to keep any deposition material from being deposited on the peripheral margin of the wafer 16.
During sputter deposition, the target 12 is bombarded by plasma ions within the chamber 10 by applying an appropriate voltage to the target 12, which causes particles of target material to be ejected from the target 12 toward the wafer 16. These particles deposit on the wafer 16 to form a desired film. During the deposition, however, particles of target can also deposit on the interior surfaces of the lower and upper shields 18 and 20. Also, a portion of the particles returns to the target 12 itself.
For these reasons, after a number of wafers are processed, the sputtering shields become coated with highly stressed, brittle barrier metal films, e.g., of TiN. Without proper treatment, these films can delaminate, flake off, and shower the substrate with particles.
Thus, it is necessary to coat the shields occasionally with metal such as titanium to prevent such particulation. This process is called xe2x80x9cpasting.xe2x80x9d A pasting material, such as titanium, is sputtered around the interior of the shields 18 and 20 along with the target 12. The layer of pasting material deposited onto the interior of the shields 18 and 20 forms a barrier to cracking and flaking between the layers of the high stress material. The pasting material such as titanium acts as a glue layer to secure the already-deposited films and to provide an adherent surface for any additional material particulate. The pasting material deposited on the target 12 must be cleaned before a normal sputtering process begins.
Conventionally, a standard shutter disk 24 and a shutter arm assembly 26 are used during pasting and cleaning of the target 12. Typically, the shutter disk 24 is housed in an enclosure 30 attached to the side of the process chamber 10. The shutter disk 24 is positioned between the pedestal 14 and the target 12 to isolate the target 12, and to protect other areas of the chamber 10 from subsequent cleaning of the target 12 and the pasting material. The shutter disk 24 is mounted on a rotating arm 32, i.e., an actuator arm, which is located outside the shield 18 and within the process chamber 10. When signaled to do so, the shutter arm assembly 26 rotates the disk 24 into the process chamber 10, overlying the wafer pedestal 14. The shutter disk 24 can then be raised into a pasting process position (at the same level as the wafer 16) by a wafer lift 34. Thus, cleaning of the target (sputtering away any contaminants present on the surface of target 12 onto the disk 24) or pasting without contaminating the surface of wafer pedestal 14 is possible because the wafer pedestal surface is protected by the shutter disk 24. When cleaning or pasting is completed, the shutter disk 24 returns to the storage position.
In semiconductor manufacturing, it is important to align a subsequent layer to a previous underlying layer. For this reason, alignment marks 37 (FIG. 2B) are typically formed on a wafer or on a reticle for alignment between various layers. The alignment marks are typically formed by etching a depth into a wafer. The alignment of one layer to the next is typically accomplished using a stepper. The stepper uses a laser beam to detect the position of the alignment marks on the wafer. It becomes difficult to maintain these alignment marks, especially in the back end of the manufacturing process, as the deposition over the marks makes the marks indistinguishable.
Recently, to protect the alignment marks from being damaged or contaminated by deposition, a two-tabbed alignment block-out scheme has been introduced. One of the process chambers incorporating the two-tabbed alignment block-out scheme is Endura Model (model number ENDURA(copyright) HP PVD(trademark)), available commercially from Applied Materials, Inc.
As illustrated in FIG. 2A, a cover ring 22xe2x80x2 has two tabs 35 protruding therefrom so that it can cover or protect alignment marks 37 of FIG. 2B on a semiconductor wafer 16xe2x80x2 during regular deposition steps. Alignment marks 37 positioned beneath the tabs 35 can be protected. As a result, the alignment marks 37 can be better maintained during deposition, and of course better alignment is possible with well-maintained alignment marks 37.
As shown in FIG. 2C, which is a cross-sectional view of a conventional cover ring taken in line 2Cxe2x80x942C of FIG. 2A, pins 38 are formed in the bottom of the cover ring 22xe2x80x2 in accordance with the two-tabbed alignment block-out scheme.
As illustrated in FIG. 2D, the cover ring 22xe2x80x2 is engaged with the lower shield 18. The pins 38 extending down from the bottom of the cover ring 22xe2x80x2 are engaged in the holes 42 in a cup 19 formed under the lower shield 18. This keeps the cover ring 22xe2x80x2 from rotating so that the cover ring 22xe2x80x2 with tabs 35 can be precisely fixed in place with respect to alignment marks 37 formed on a wafer 16.
However, conventional tabbed alignment block-out hardware with the cover ring 22xe2x80x2 and the lower shield 18 cannot use a standard shutter disk and shutter arm assembly because the pins 38 of the cover ring 22xe2x80x2 would interfere with the shutter disk 24 as indicated at 27 of FIG. 1. Particularly, if an actuator arm 25 were to attempt to put the shutter disk 24 onto the wafer pedestal 14, the shutter blade 32 would run into the pins 38 extending down from the lower shield 18.
Thus, there would be a clearance problem underneath the lower shield 18 if the shutter disk 24 were used with the two-tabbed block-out scheme.
Further, because the shutter disk 24 has to be sufficiently thick (to withstand various processing conditions), it can be inadvertently adhered to the tabs 35 by deposition during the pasting or the cleaning steps as illustrated in FIG. 3. Therefore, production wafers instead have been used for pasting by transferring the production wafers into the chamber and pasting on the wafers to avoid the clearance and gluing problems.
Unfortunately, using expensive production wafers each time to paste the chamber (which is required before each production lot) is costly and time consuming. Particularly, this is true because operator intervention is necessary to place an extra wafer in each production lot, leading to otherwise unnecessary exposure to mis-processing and it takes a long time to transfer the wafer to the chamber to be pasted. Also, because pasting is required quite often for the PVD chamber, a large number of production wafers can be wasted. Alternatively to using a wafer for pasting, an additional chamber having a metal disk for shuttering can be attached to the main chamber body and a robot arm can be used to pick up the disk and to transfer it to the chamber for pasting or cleaning of the target.
However, these prior art methods for cleaning targets or pasting deposition chambers significantly reduce throughput because they require significant non-productive down-time to transfer paste wafers from another location into the chamber for pasting. Also, in addition to the down time to transfer the metal disk to the pasting or the cleaning position, the metal disk for shuttering can stress the robot arm joints, thereby wearing out the robot arm assembly.
Accordingly, a need remains for a new sputtering apparatus that allows the use of a shutter and shutter arm assembly that do not require long down time to transfer a wafer or a shutter disk into the pasting or cleaning position, thereby improving the throughput without problems noted above.
The present invention provides a new sputtering apparatus that allow the use of a shutter disk and shutter arm assembly for pasting in a two-tab blockout scheme, thereby improving productivity and reducing waste of production wafers.
According to the present invention, physical vapor deposition (PVD) system comprises
a chamber, an upper shield and a lower shield mounted within the chamber, a cover ring having one or more tabs extending radially inwardly therefrom. The PVD system further includes a shutter disk having one or more notched areas formed in the periphery thereof to receive the one or more tabs of the cover ring. The cover ring has two or more recesses formed in an upper side thereof with a guide pin extending from the center of the recesses. The lower shield has two or more cups with a hole therein to be engaged with the guide pin of the cover ring to keep the lower shield from rotating with respect to the cover ring. The cups of the lower shield are inserted into the recesses of the cover ring. A wafer pedestal is mounted within the chamber. Additionally, the PVD system includes means for rotating the shutter disk to place the shutter disk on the wafer pedestal; and means for vertically adjusting the height of wafer pedestal.
With the shutter disk having notched areas and the modified cover ring, the present invention allows use of the shutter disk and shutter arm assembly without a clearance problem underneath the lower shield and without a gluing problem in a tabbed alignment block-out scheme. Thus, the present invention can be fully automated and significantly improve productivity.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention that proceeds with reference to the accompanying drawings.